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Report on Poas (Costa Rica) — July 1985

Scientific Event Alert Network Bulletin, vol. 10, no. 7 (July 1985)
Managing Editor: Lindsay McClelland.

Poas (Costa Rica) Fumarole temperatures drop

Please cite this report as:

Global Volcanism Program, 1985. Report on Poas (Costa Rica). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 10:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198507-345040.

Volcano Profile |  Complete Bulletin


Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Activity was characterized by the emission of gas from fumaroles on the eroded 1953-55 cone. Fumarole temperatures continued to drop, while crater lake temperature remained constant (table 3).

Table 3. Temperatures (in °C) measured in a fissure on the E side of the eroded 1953-55 cone and in the crater lake, January 1982-October 1985.

Date Fumarole Temperature Crater Lake Temperature Lake Water pH
Jan 1982 860 47 --
Feb 1982 883 48 --
Mar 1982 887 47 --
Apr 1982 873 50 --
Dec 1982 731 40 --
Jan 1983 753 56 --
Feb 1983 732 60 --
Mar 1983 780 60 --
Apr 1983 818 60 --
May 1983 832 57 0.06
Jun 1983 834 57 0.1
Jul 1983 822 57 0.2
Aug 1983 806 58 0.2
Sep 1983 810 58 0.3
Oct 1983 801 60 0.6
Nov 1983 750 58 --
Dec 1983 750 56 0.07
Jan 1984 690 51 0.7
Feb 1984 650 51 --
Mar 1984 570 54 0.7
Apr 1984 570 49 --
May 1984 586 50 --
Jun 1984 603 50 --
Jul 1984 602 48 --
Aug 1984 530 48 --
Sep 1984 500 50 --
Oct 1984 490 48 --
Nov 1984 510 48 --
Dec 1984 515 48 --
Jan 1985 550 44 --
Feb 1985 560 44 --
Mar 1985 584 44 --
Apr 1985 568 44 --
May 1985 490 44 --
Jun 1985 420 48 --
Jul 1985 316 46 --
Aug 1985 295 45 --
Sep 1985 294 45 --
Oct 1985 310 45 --

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: J. Barquero H. and E. Fernández S., Univ. Nacional, Heredia.